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Communications Materials

Epitaxial superconductor/semiconductor/metal nitride heterostructure for single-photon detection

Shangjr Gwo, Chang-Wei Cheng, Yan-Jyun Liao, Yun-Tai Shih, Ya-Yu Li, Chi-Sung Lin, Hsi-Hsin Chen

Published Oct 29, 2026• 0 citations
Publisher

Abstract

Abstract Superconducting nanowire single-photon detectors (SNSPDs) have become increasingly important for both classical and quantum applications requiring single-photon sensing. Most current SNSPDs based on superconducting niobium nitride (NbN) ultrathin films are fabricated utilizing polycrystalline or amorphous superconductor films, and film inhomogeneity and defectivity can cause significant issues. Here, we present an all-epitaxial approach for fabricating SNSPDs with integrated metal reflectors, semiconductor (dielectric) resonators, and superconductor nanowire detectors. A working example is realized by molecular-beam epitaxy growth of a tri-layered heterostructure, consisting of a titanium nitride (TiN) reflector with ~ 92% reflectivity at the telecommunication wavelength (1550 nm), an aluminum nitride (AlN) resonator with a broad optical transparency window, and a NbN nanowire on c -plane sapphire wafer. The all-epitaxial approach provides a manufacturable platform with superior material properties, as well as uniformity across the wafer, which manifest themselves in tunable material parameters of the superconducting nanowire, including normal-state resistance, superconducting critical temperature, superconducting critical current, and kinetic inductance. The optimized material properties can be utilized to achieve excellent SNSPD performance, including wafer-scale uniformity in device characteristics and broadband (~300 nm) system detection efficiency (>90%) centered at 1550 nm, suitable for large-scale detector arrays and wavelength-division multiplexing (WDM) applications.

DOI
10.1038/s43246-026-01419-z

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Abstract Superconducting nanowire single-photon detectors (SNSPDs) have become increasingly important for both classical and quantum applications requiring single-photon sensing. Most current SNSPDs based on superconducting niobium nitride (NbN) ultrathin films are fabricated utilizing polycrystalline or amorphous superconductor films, and film inhomogeneity and defectivity can cause significant issues. Here, we present an all-epitaxial approach for fabricating SNSPDs with integrated metal reflectors, semiconductor (dielectric) resonators, and superconductor nanowire detectors. A working example is realized by molecular-beam epitaxy growth of a tri-layered heterostructure, consisting of a titanium nitride (TiN) reflector with ~ 92% reflectivity at the telecommunication wavelength (1550 nm), an aluminum nitride (AlN) resonator with a broad optical transparency window, and a NbN nanowire on c -plane sapphire wafer. The all-epitaxial approach provides a manufacturable platform with superior material properties, as well as uniformity across the wafer, which manifest themselves in tunable material parameters of the superconducting nanowire, including normal-state resistance, superconducting critical temperature, superconducting critical current, and kinetic inductance. The optimized material properties can be utilized to achieve excellent SNSPD performance, including wafer-scale uniformity in device characteristics and broadband (~300 nm) system detection efficiency (>90%) centered at 1550 nm, suitable for large-scale detector arrays and wavelength-division multiplexing (WDM) applications.
Superconducting nanowires used in single-photon detectors have been realized on amorphous or poly-crystalline films. Here, we report the first use of single-crystalline NbN thin films for superconducting nanowire single-photon detectors (SNSPDs). Grown by molecular beam epitaxy (MBE) at high temperature on nearly lattice-matched AlN-on-sapphire substrates, the NbN films exhibit a high degree of uniformity and homogeneity. Even with relatively thick films, the fabricated nanowire detectors show saturated internal efficiency at near-IR wavelengths, demonstrating the potential of MBE-grown NbN for realizing large arrays of on-chip SNSPDs and their integration with AlN-based χ(2) quantum photonic circuits.
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Superconducting nanowire single-photon detectors (SNSPDs) are the leading technology for low noise, high efficiency infrared single-photon detection. The basic SNSPD consists of a nanowire patterned in an ultrathin superconducting thin film, which is cooled below its critical temperature and biased close to its critical current. The absorption of a single-photon creates a resistive region, triggering a fast output voltage pulse which can be readily amplified and registered. The excellent performance of SNSPDs at near-infrared and telecommunications wavelengths has led to their adoption in important applications such as quantum secure communications, single-photon spectroscopy and single-photon LIDAR. A clear challenge for the SNSPD community is to extend the spectral range of SNSPDs into the mid infrared, and to improve material uniformity to enable the realization of large area arrays for multimode or free space coupling. The aim of this work is to evaluate potential materials for next generation mid-infrared SNSPD arrays. In this work, thin films of polycrystalline NbN and amorphous MoSi have been optimized to test the uniformity of a multipixel array configuration composed of 8 nanowire meander structures covering 10 um x 10 um area, 100 nm width and 50% filling factor. The 8-pixels SNSPD arrays have been patterned on 8 nm thickness NbN grown on high resistivity silicon (HR Si) substrate at room temperature and at 800 °C exhibiting respectively 4.4 K and 7.3 K as mean critical temperature across the pixels. The 8- pixels SNSPD array patterned on 8 nm thickness MoSi cooling the HR Si substrate to -180 °C has exhibited a mean critical temperature of 3.2 K across the pixels. Optical properties have been measured by an attenuated 1550 nm laser diode source delivered by single mode optical fibre at a controlled distance from the chip in order to broadly illuminate the array. The optical properties have been studied only for the 8 nm thickness NbN SNSPD array grown at room temperature has demonstrated uniform optical properties across pixels exhibiting similar saturation of the internal efficiency over a large bias, similar dark count rate and similar timing jitter (about 137 ps) across pixels. In the single photon regime at 1550 nm, pixels 4 and 6 of the 8 nm thickness NbN SNSPD array exhibit 28.4% and 4.7% pixel detection efficiency as measured at the bias current 95% of their respective critical current at 2.2 K.
We report the fabrication of superconducting nanowire single-photon detector (SNSPD, SSPD) based on molybdenum nitride (MoN) film with and without a cavity structure. Ultrathin polycrystalline γ-Mo2N films with aTcabout 6 K were obtained by reactive DC magnetron sputtering. The absorption efficiency of the device was calculated by the finite-difference time-domain (FDTD) method using the optical constants of MoN determined by ellipsometry measurements. The SNSPD with a meander of 150-nm-width and 7-nm-thick nanowire showed a long saturation plateau in the bias current dependence of the system detection efficiency (SDE) at visible wavelength. The SNSPD with a cavity structure showed an SDE of 37% and a timing jitter of 79 ps at a wavelength of 1560 nm. The results show that MoN is a promising alternative to amorphous superconductors for high-performance SNSPD.
High-quality ultrathin films of niobium nitride (NbN) are developed by the plasma-enhanced atomic layer deposition (PEALD) technique. Superconducting nanowire single-photon detectors patterned from this material exhibit high switching currents and saturated internal efficiencies over a broad bias range at a telecommunication wavelength of 1550 nm. Statistical analyses on hundreds of fabricated devices show a near-unity throughput yield due to the exceptional homogeneity of the films. The ALD-NbN material represents an ideal superconducting material for fabricating large single-photon detector arrays combining high efficiency, low jitter, and low dark counts.
Abstract This paper presents the development of a superconducting nanowire single-photon detector (SNSPD) integrated into a distributed Bragg reflector (DBR) with a design center wavelength of 830 nm and a bandwidth of 200 nm. This SNSPD is made of a superconducting niobium nitride (NbN) thin film that is produced using plasma-enhanced atomic layer deposition. The DBR is made of 15 alternating layers of silicon nitride and silicon oxide that are produced through plasma-enhanced chemical vapor deposition. The reflection efficiency of the mirror is 90% at a wavelength of 830 nm. For sufficient optical coupling, an optical micro-connector optimized for multimode or single-mode optical fibers with a diameter of 128 μm was formed using two-photon polymerization techniques. The niobium nitride film was deposited onto the DBR surface in-situ in two separate reactors connected by a vacuum transfer. The in-situ technique of deposition of a superconducting niobium nitride film and a DBR has allowed achieving a system detection efficiency of 90% at a wavelength of 830 nm and a dark count rate of 10 s−1 at a temperature of 2.5 K. Additionally, the detector jitter was 50 ps.